This module makes the operations exported by System.Posix.Unistd
available on all platforms. On POSIX systems it re-exports operations from
System.Posix.Unistd, on other platforms it emulates the operations as far
as possible.

GHC Note: Control.Concurrent.threadDelay is a better choice.
Without the -threaded option, usleep will block all other user
threads. Even with the -threaded option, usleep requires a
full OS thread to itself. Control.Concurrent.threadDelay has
neither of these shortcomings.